The present invention relates to a two cycle engine and more particularly to a two cycle engine which includes a subchamber at the exhaust port and a reed valve unit in the inlet port.
As is generally known, increased output from two cycle engine is achieved by increased intake and exhaust efficiencies and increased charging efficiency of intake air. To improve exhaust efficiency there has been hitherto made such an arrangement that two cycle engine has a subchamber disposed at the exhaust port in communication with the latter and a poppet valve adapted to open and close at the same cycle as a predetermined number of revolutions of engine is interposed between the subchamber and the exhaust port. As the poppet valve opens and closes in that way, communication between the subchamber and the exhaust port is alternately established and interrupted so that the optimum volume of exhaust tube is assured in dependence on the existing rotational speed area of engine.
On the other hand, to improve intake efficiency there has been hitherto fixedly arranged a reed valve unit in the inlet port. This reed valve unit is intended to inhibit occurence of backward flowing of combustible mixture toward the inlet port under the influence of movement of a piston after the mixture is sucked into the crank case, that is, occurence of so-called "blow-back phenomenon" so as to improve suction efficiency mainly in the lower rotational speed area.
To meet requirement for improved efficiency the conventional two cycle engine employs a poppet valve adapted to alternately establish and interrupt communication between the exhaust port and the subchamber in the above-described manner. Since the poppet valve is constructed so as to interrupt communication between the exhaust port and the subchamber with the aid of resilient means such as coil spring or the like when engine is rotated at high rotational speed, the poppet valve fails to be brought in tight contact with valve seat in the higher rotational speed area as it resonates due to vibration of engine. Thus, the exhaust port becomes communicated with the subchamber, resulting in reduced output from engine in the higher rotational speed area.
Further, the conventional two cylce engine has a reed valve unit fixedly disposed in the inlet port so that improved intake efficiency is assured in the lower rotational speed area. However, it has been found as a drawback inherent to the conventional engine that as it is operated at higher rotational speed, there takes place resonance due to low natural frequency of vibration of the reed valve unit and thereby timing fluctuates when the reed valve unit opens and closes the inlet port, resulting in reduced intake efficiency in the higher rotational speed area and reduced output from engine.